Process for impregnating webs with polymer solutions

ABSTRACT

1. A PROCESS FOR THE UNIFORM IMPREGNATION OF A FIBROUS MAT WITH A POLYMER SOLUTION COMPRISING THE STEPS OF PASSING A FIBROUS MAT HAVING A SURFACE THROUGH A SUCCESSION OF SUBSTANTIALLY IDENTICAL GAPS EACH DEFINED BETWEEN PAIRS OF ROLLERS, COATING SAID ROLLERS UNIFORMLY AND CONSTANTLY WITH SAID POLYMER SOLUTION, THE GAPS BETWEEN SAID ROLLERS BEING SUCH THAT SAID FIBROUS MAT IS NOT SUBJECTED TO COMPRESSION THEREBETWEEN BY THE ROLLERS PER SE, MAINTAINING THE CLEARANCE OF SAID GAPS EQUAL TO OR GREATER THAN THE THICKNESS OF SAID MAT, DRIVING EACH OF SAID COATED ROLLERS IN THE SAME DIRECTION AS THE ADVANCING DIRECTION OF THE FIBROUS MAT AT A SPEED AT LEAST TWO TIMES FASTER THAN THE SPEED AT WHICH SAID FIBROUS MAT ADVANCES, AND TRANSPORTING A UNIFORM STREAM OF SAID POLYMER SOLUTION TO SAID MAT ON ITS SURFACE TO IMPREGNATE SAID MAT.

Oct 11 11 1974 mm ENOMOTO PROCESS FOR IMPREGNATING WEBB WITH POLYMERSOLUTIONS QriginaIFiled Aug. 4, 1969 FlG- -i United States Patent3,843,389 PRQCESS FOR IMPREGNATING WEBS WITH PGLYMER SOLUTIONS YuyaEuomoto, Kurashiki, Japan, assignor to Kurashiki Rayon (30., Ltd,Kurashiki, Japan Continuation of application Ser. No. 847,359, Aug. 4,1969, which is a continuation-in-part of application Ser. No. 539,843,Apr. 4, 1966, both now abandoned. This application Mar. 8, 1972, Ser.No. 232,982

Int. Cl. BilSc 9/04; B44d 1/02 U.. Cl. 1ll7--68 2 Claims ABSTRACT BF THEDISCLOSURE A process is disclosed for impregnating a polymer solutioninto a fibrous mat by using a succession of gaps between pairs ofrollers which are wide enough apart to prevent compression of thefibrous mat. 'Ihe rollers are driven in the same direction as theadvancing direction of the fibrous mat at a speed at least twice as fastas the advancing speed of the mat. The use of such a speed permits 100%impregnation.

This application is a continuation of Ser. No. 847,359, filed Aug. 4,1969 and now abandoned, which in turn is a continuation-in-part ofapplication Ser. No. 539,843, filed Apr. 4, 1966 and now abandoned.

The present invention relates to a novel process for impregnatingfibrous mats such as webs, non-woven cloths formed of fibrous materialsand felts with polymer solutions.

Usually, for impregnation of such materials with polymer solutions,either a stationary process or dip process is employed. The formerconsists of floating a fibrous mat on the surface of a polymer solution,whereby the solution can fully permeate through the inside of the masswith relative uniformity owing to capillary ascending action of thesolution. However, the higher the viscosity of the polymer solution, thelonger the time required for thoroughly impregnating a fibrous mat withthe solution, and sometimes it is highly difiicult to attain thoroughimpregnation. The latter is a process for dipping a fibrous mat in apolymer solution, in many cases with an additional step of compressionwith rollers, whereby relatively thorough impregnation is effected.However, this often results in application of unnecessary compressiveforce upon the fibrous mat to effect adversely the properties of thematerial after the process. Further, as the viscosity of the polymersolution is increased the number of pores formed in the fibrous mat isincreased due to accumulation of bubbles in the solution and ununiformimpregnation.

It is an object of the present invention to provide a novel processwhich overcomes the disadvantages of known processes.

The present invention consists in a process for the impregnation of afibrous mat with a polymer solution, in which a fibrous mat is passedbetween a pair of parallel rollers, the gap between which being suchthat the fibrous mat is not subjected to compression therebetween, atleast one of said rollers being driven in the same direction as that thefibrous mat advances at a speed faster than the fibrous mat advances andtransporting on its surface a uniform stream of the said polymersolution to the surface of the said mat.

The invention is further illustrated with reference to the accompanyingdrawings, in which:

FIG. 1 is a side view illustrating the basic conception of the presentinvention; and

FIG. 2 is a side view of a preferred embodiment of the inventioncorresponding to FIG. 1.

Patented Get. 22, 1974 Basically the process of the invention comprisesadjusting the clearance between a pair of rollers to a value equal to orgreater than the thickness of a fibrous mat, revolving the rollers 2,2', in the same direction as the advancing direction of the fibrous matll shown in FIG. 1, supplying a predetermined amount of a polymersolution 3, 3' uniformly and constantly on the rollers, and thusimpregnating the fibrous mat with the polymer solution. The advancingdirection of the fibrous mat is necessarily the same as the runningdirection of the rollers 2, 2'. It is preferred to revolve the roller ata speed 2 times or more faster than that of the advancing fibrous mat.In FIG. 1, numerals 4, 4' designate drainers for controlling the supplyof polymer solution. In the practical application of the invention, thenumber of rollers is not confined to a pair but a multi-stage rollerarrangement as shown in FIG. 2 may be used to effect repetition ofimpregnation depending on the required amount of impregnant. It ispreferred to use at least four-stage roller arrangement. Control of theamount of the solution impregnating the fibrous mat can be optionallyvaried by adjusting the amount of the polymer solution to be supplied toeach roller, because there is a certain relationship among the amount ofthe polymer solution to be supplied, the number of impregnation cyclesemployed, and the amount to be actually impregnated, with respect to theimpregnation tendency of the polymer solution. Further, in order tocarry out the maximum impregnation of a fibrous mat, the clearancebetween the rollers must be greater than the thickness of the fibrousmat, because if the roller clearance is less than the thickness of mat,a sufficient impregnation effect cannot be achieved. Moreover, accordingto the impregnation process of the invention, the temperature of polymersolution can be controlled easily through control of the rollertemperatures with a heating medium.

While in the impregnation process above described a fibrous mat isimpregnated with a polymer solution fed simultaneously from a pair ofopposite rollers (2, 2' in FIG. 1), it is also possible to supply thepolymer solution to only one of the rollers and to impregnate thefibrous mat from only one side thereof. In the latter case, the timerequired to impregnate thoroughly the fibrous mat with the polymersolution is of course prolonged, and the necessary number of rollerstages is increased. However, depending on the intended purpose of themat, it is sometimes necessary to impregnate a fibrous mat partiallywith a polymer solution or to keep the mat from being fully impregnated.In such case, the impregnation from only one side of the mat iseffective.

The process of the invention can be carried out even when the solutionto be used for the impregnation contains minute pigment particles, finepower of synthetic or natural high molecular weight polymer, or finepowder of organic or inorganic substance, which is insoluble in thesolvent, in a dispersed state.

Now the impregnation process of the invention is illustrated by thefollowing examples.

Example I A needle-punched web formed of mixed-spun fibres of nylon-6and polystyrene at a ratio of 45:55 (which web weighed 350 g./m. and hada specific gravity of 0.20) was impregnated with a solution ofpolyurethane in dimethyl formamide by the use of a four-stage rollerunit in accordance with the impregnation process of the invention. Theresults as classified by the viscosity of polymer could accomplishthorough impregnation in a short time regardless of the viscosity of thesolution used.

The polyurethane used was prepared by reacting polybutylene adipateglycol, diphenyl methane diisocyanate and 1.4-butylene glycol. 5

TABLE 1 Type of polymer solution (percent) Gone. 22%, 25

Gone. 22%, 46

Gone. 22%, 86 Gone. 26%, 350

i The time required represents the period during which the web passedthrough the four states of rollers, hence depending on the velocity ofthe web. In this case, the velocity at which the web passed was 3m./min.

3 The time required represents the period during which the web wasfloated on the surface of a polymer solution and was impregnatedcompletely across the entire section.

Example 2 Woollen felt (weighing 320 g./m. with a specific g5 gravity of0.25) was impregnated with a solution of the 3 This represents themaximum amount of impregnant of the web, calculated by the formula:Magnification of impregnation= (weight of web after impregnation)(weight of web before impregnation) (weight of web before impregnation)The viscosity is the value determlncd at 30 C. 5 The magnificationofimpregnation after dipping for one hour was 3.9.

tionary process. In Table 3, there are shown the comparative results interms of the periods of time required and magnifications ofimpregnation.

TABLE 3 Type of polymer solution Gone. 22% Gone. 22%, Gone. 26%, Processof impregnation Item measured 25 poises 86 poises 630 poises RemarksTime required Within 1 min Within 1 min Within 1 min. Process of theinvention ig of impregnation 4] g 6 i H Roller temp.. 30 C.

- iine required 5 min 0 min ver r. o

p pwcess of impregnation U 4.6 i i o p y SOL 30 *The magnification ofimpregnation alter dipping for one hour was 3.0.

polyurethane described in Example 1 in dimethyl formamide by the use ofa four-stage roller unit in accordance with the invention, and theresults were compared with those attained by the conventional dipprocess which combined with compression with rollers. The process of theinvention permitted the felt to be impregnated uniformly What is claimedis: ii. A process for the uniform impregnation of a fibrous mat with apolymer solution comprising the steps of passing a fibrous mat having asurface through a succession of substantially identical gaps eachdefined between pairs of rollers,

without bubbles, whereas the dip process caused accumulacoating saidrollers uniformly and constantly with said tion of bubbles in theimpregnating solution, which in polymer solution, the gaps between saidrollers being turn increased the number of pores in the felt, thus keepsuch that said fibrous mat is not subjected to coming the magnificationof impregnation at a low level. I pression therebetween by the rollersper se,

The results are shown in Table 2. maintaining the clearance of said gapsequal to or TABLE 2 Type of polymer solution Gone. 22% Gone. 22% Gone.26%

Process of impregnation 25 poises 8G poises 350 poises RemarksMagnification of impregnation by the process of the invention 4. 0 4. 04. 0 Roller temp; 30 C. Magnification of impregnation by the dip process3. 8 3.8 3. 6 Temp. of polymer so1.: 30 C.

Example 3 Non-woven cloth of 6-nylon fibres (weighing 400 g./m. with aspecific gravity of 0.21) was impregnated with a greater than thethickness of said mat, driving each of said coated rollers in the samedirection as the advancing direction of the fibrous mat at a 5 6 speedat least two times faster than the speed at 2,119,480 5/1938 Codwise117-111 F which said fibrous mat advances, and 2,396,946 3/1946 Grupe118-249 transporting a uniform stream of said polymer solution 2,582,40711/ 1952 Barrett et al 117-111 F to said mat on its surface toimpregnate said mat. 2,624,914 11/ 1953 Rhodes 117-111 F 2. The processof claim 1, wherein said succession of 5 2,700,620 11/1955 Somers118-227 gaps comprises at least four pairs of rollers. 3,029,780 4/1962Justus et a1 118-249 3,257,226 6/1966 Thwaites 117-111 F ReferencesCited 1,517,606 12/1924 Wiese 117 111 F 1,928,568 9/1933 Loomis 117-111R2,013,312 9/1935 Supligeau e161.-- 117-111F1174111911MORA118227'249*451424

1. A PROCESS FOR THE UNIFORM IMPREGNATION OF A FIBROUS MAT WITH APOLYMER SOLUTION COMPRISING THE STEPS OF PASSING A FIBROUS MAT HAVING ASURFACE THROUGH A SUCCESSION OF SUBSTANTIALLY IDENTICAL GAPS EACHDEFINED BETWEEN PAIRS OF ROLLERS, COATING SAID ROLLERS UNIFORMLY ANDCONSTANTLY WITH SAID POLYMER SOLUTION, THE GAPS BETWEEN SAID ROLLERSBEING SUCH THAT SAID FIBROUS MAT IS NOT SUBJECTED TO COMPRESSIONTHEREBETWEEN BY THE ROLLERS PER SE, MAINTAINING THE CLEARANCE OF SAIDGAPS EQUAL TO OR GREATER THAN THE THICKNESS OF SAID MAT, DRIVING EACH OFSAID COATED ROLLERS IN THE SAME DIRECTION AS THE ADVANCING DIRECTION OFTHE FIBROUS MAT AT A SPEED AT LEAST TWO TIMES FASTER THAN THE SPEED ATWHICH SAID FIBROUS MAT ADVANCES, AND TRANSPORTING A UNIFORM STREAM OFSAID POLYMER SOLUTION TO SAID MAT ON ITS SURFACE TO IMPREGNATE SAID MAT.